In known apparatus for monitoring the correct operation of the alternator and the associated regulator in a motor vehicle or other mobile unit, a control lamp is provided which is connected between the B+ bus of the electrical supply system to which the positive terminal of the battery is also connected and the regulator input which is connected to the common connection of the exciter diodes. The control lamp will be lit if the ignition switch is closed when the automobile is stationary and there is therefore no generator output, since in that case the positive side of the battery is connected to one side of the lamp while the negative side of the battery is connected through the field winding and the regulator to the D- terminal.
In some known systems, a thermal voltmeter is connected between the B+/D- terminals.
In other known systems, an ammeter is connected between the positive side of the battery and the positive bus of the vehicle, although bypassing the starter terminal, so that lack of proper operation of the generator or regulator is indicator by a constant discharge current. Usually, the regulator input to which the exciter diodes are connected has the designation D+; the regulator output connected to the field or exciter winding of the generator is denoted by DF; the positive and negative terminals of the supply system are designated by B+ and B-, respectively, the regulator terminal D- corresponding to the B- terminal of the supply. These designations will be used throughout this specification.
It is a disadvantage of the above-described apparatus that certain malfunctions, for example a short circuit or an open circuit in the main transistor in the regulator cannot be recognized. Other malfunctions such as a short circuit or a break in the rectifier diodes, which can later lead to a complete malfunction of the generator can also not be recognized since the control lamps are not sufficiently sensitive. The control lamp will, for example, not react to a short circuit in the main regulator transistor at all, even though in this case a very substantial increase in the supply voltage with resultant overheating of the battery can result. Further, the control lamp requires a particular operating voltage and operating current.